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Olopatadine, a new second-generation antihistamine, is widely used in the treatment of allergic disorders. The low levels of histamine H1 receptor occupancy in human brain by olopatadine, which is related to its minimal sedation, suggest its low penetration into the brain. The present study evaluates the impact of P-glycoprotein (P-gp) on brain penetration and plasma concentration of olopatadine. The uptake amount of olopatadine in human P-gp transfected LLC-PK1 cells (LLC-GA5-COL150) was lower than that in LLC-PK1. The uptake of olopatadine in LLC-GA5-COL150 was increased in the same level as that in LLC-PK1 in the presence of cyclosporine A, a P-gp inhibitor. After intravenous or oral administration of olopatadine to wild type (WT) and mdr1a/1b knockout (KO) mice at a dose of 1 mg/kg, the brain concentration in KO mice was higher than that in WT mice. On the other hand, the plasma concentration of olopatadine after either route of administration was not different between WT and KO mice. These results suggest that olopatadine is a substrate of P-gp, and that P-gp limits the brain penetration but dose not affect the plasma concentration of olopatadine.

Benidipine, which is a calcium channel blocker that has clinical advantages in the treatment of hypertension, is metabolized by CYP3A4 in humans. The effect of benidipine on the metabolism of simvastatin by human liver microsomes was investigated in order to predict the potential of in vivo drug-drug interactions between benidipine and other substrates of CYP3A4. The results were compared with data generated with azelnidipine, which is also metabolized by CYP3A4. Both benidipine and azelnidipine inhibited simvastatin metabolism in vitro in a concentration-dependent manner. Assuming competitive inhibition, the K(i) values based on the unbound concentrations, were calculated to be 0.846 and 0.0181 microM for benidipine and azelnidipine, respectively. If simvastatin (10 mg) and benidipine (8 mg, the clinically recommended highest dose) were to be administered concomitantly, the ratio of the areas under the concentration-time curves of simvastatin with and without benidipine (AUC((+I))/AUC) was predicted to be 1.01. On the other hand, if simvastatin (10 mg) and azelnidipine (8 mg) were co-administered, the AUC((+I))/AUC for simvastatin was predicted to be 1.72, which is close to the observed value (1.9) in healthy volunteers. These data suggest that benidipine is unlikely to cause a drug interaction by inhibiting CYP3A4 activity in the liver.

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